The physician knows that just as there can be merely imagined illness, so too is there merely imagined health. For the latter, therefore, he takes the first measures that will bring the illness to view.
– Soren Kierkegaard, The Sickness unto Death (53)

In SUD Kierkegaard outlines various sicknesses or states of despair that affect the spirit. According to Kierkegaard no one is free from despair, not even one. Yet there are different kinds of despair. The most horrific form that despair takes is that which is hidden, ‘so concealed in a person that he himself is not aware of it!’ (57) This person lives their life unaware of their ‘spiritual’ state and looks on their existence as a series of particular moments or actions, but not with a ‘conception of an infinite consistency in themselves.’ (140) That is they have no understanding of their spiritless existence of their being but only consider the external. So they live with either ‘child-like naivety, or with empty mindedness’ (140) weighing up ‘particular good deeds’ against ‘particular sins’. For this person the scales will always tip toward the former and they will then be at ease. But our sins of action are to the state of our spiritual health what the puffs of smoke coming from a locomotive are to the engine.

In SUD and The Concept of Anxiety Kierkegaard (or Anti-Climacus and Haufniensis) is trying to remind his apathetic and nominally Christian contemporaries of their sinfulness so that they are motivated to be saved. If you don’t think you sin then you won’t think you need to be saved. Kierkegaard as physician is trying to tell the sick man who claims to be healthy that he is in fact ill and in need of attention.